Most modern distros are either new distro trying to have more modern sensibilities, distros based off of Debian, Arch, or Fedora, or occasionally original things that are okay with being superficially similar to one of those while doing things differently at lower levels. OpenSUSE is one of the few remaining distros from the olden days that has been independent and doing their own thing for decades without spawning a bunch of forks or dying off. If you want to try something even older and crazier Slackware is sure an experience.